We can't underscore enough how cray things were in Germany of the 1930s. You had Hitler as chancellor, rampant anti-Semitism, and the Nazi's unstoppable propaganda machine. Go rent Triumph of the Will if you don't know what we're talking about. Those National Socialists really knew how to make evil look good—on film, in graphics, you name it.
So Benjamin came along with his "Work of Art" essay and said, "Hey, you fascists aren't the only ones who get to use art for political ends!" As the closing sentence of his essay declares, the loss of that pesky aura was a real game changer: "Instead of being based on ritual, [art] begins to be based on another practice—politics." Boom.